IR reflective elements made of impact-resistance plastic, and a process for their production

ABSTRACT

A process for the production of a translucent, IR-reflective plastic element, consisting entirely or at least in part of an impact-resistant, thermoplastic plastic, containing IR-reflective particles made of a lamellar-shaped carrier pigments coated with a metal oxide and the plastic element made therefrom.

BACKGROUND OF INVENTION

1. Field of the Invention

The present invention relates to IR-reflective elements made ofimpact-resistant plastic, and a process for their production.

2. Discussion of the Background

The use of disks of polymethyl methacrylate containing light-reflectiveparticles aligned parallel to a surface is described in DE 25 44 245.The pigment particles used cause a selective reflection in the infraredrange, which can be characterized by a selectivity number of greaterthan 1. TiO₂, lead carbonate, and bismuth oxychloride are mentioned asIR-reflective pigments. The use of anatase-type TiO₂ pigments,precipitated onto mica laminae, is described. Further, a layer ofanatase-type TiO₂ pigment having a thickness of approximately 120 μm isemphasized as being particularly advantageous.

The particles as described in DE 25 44 245 are dispersed in a partiallypolymerized methyl methacrylate to form a suspension at a concentrationranging from 0.01 to 1 wt. %. Thereafter, the suspension is fullypolymerized, producing polymethyl methacrylate, in a chamber betweenglass plates. If the chamber is positioned horizontally, thepigment-mica particles of the suspension align parallel to the disksurface as they drop. This phenomenon yields fully polymerized diskshaving the desired IR-reflective effect. This parallel alignment of theIR-reflective particles can be improved if the glass plates of thechamber are moved several times in a circular motion relative to oneanother while the polymerizing material is still in a gel state.

DE 25 44 245 describes the possibility of working IR-reflective pigmentsinto molding masses. The pigments then align parallel to the surfacewhen the masses are processed using calendering, extrusion, orinjection-molding.

EP-A 0 548 822 describes translucent, IR-reflective elements having asun-protection and heat-insulation effect. These elements includesheets, web plates, and domelights. The elements have a transmission, T,in the visible spectrum ranging from 45 to 75%. The transmission isdefined as the degree of light transmission for daylight, i.e. standardlight type D65 or T_(D65). They also have a total energy transmissiondegree, g, ranging from 30 to 60%. Further, they have a ratio of T/g,i.e. T_(D65)/g, at least 1.15. These measurements result from thoseexperiments described according to DIN 67 507.

The translucent, IR-reflective elements of EP-A 0 548 822 can beproduced from a rigid, amorphous base material made of translucentplastic and a translucent coating material containing from 20 to 40 wt.% of IR-reflective particles. The IR-reflective particles consist of alayer of titanium dioxide. The titanium layer is present at a thicknessranging from 60 to 120 nm on a lamellar-shaped carrier pigment, and isformed by co-extrusion or coating processes. Coating processes includelacquering or reverse-roll-coating. A coating layer that is 5 to 40micrometers thick and contains the IR-reflective particles adheres tothe base material made of a transparent binder not soluble in water. TheIR-reflective particles are aligned parallel to the surface of the basematerial.

In the examples of EP-A 0 548 822, rutile type TiO₂ pigments are used.EP-A 0 548 822 recommends the selection of a binder for theIR-reflective layer that has a lower melt viscosity than that of thebase material for co-extrusion. In order to prevent the pigments frombreaking, a twin-screw extruder having closely interlocking screws thatrotate in opposite directions is used, and the pigment is workeddirectly into the melt.

Multi-web plates made of polymethyl methacrylate having a co-extrudedIR-reflective finish are commercially available according to EP-A 0 548822. Further, multi-web plates made of polycarbonate having acorresponding IR-reflective finish are known to improveweather-resistance. Here, another co-extruded layer containingUV-absorbers is located on the co-extruded pigment layer.

DE 196 569 A1 describes multi-layer interference pigments consisting oftransparent carrier materials that are coated with alternating layers ofmetal oxides having a low and a high index of refraction, where thedifference between the indices of refraction is at least 0.1.Accordingly, an alternating layer of TiO₂/SiO₂/TiO₂ can be placed onmica laminae. The pigments described in DE 196 18 569 A1 are suitablefor pigmentation of agricultural films in order to keep out infraredradiation from the sun, thereby preventing excessive heating ofgreenhouses.

EP-A 0 733 754 describes multi-web plates made of a polymethylmethacrylate modified to be impact-resistant. Depending on the impactresistance of the material used and the minimum thickness of the topflange of the multi-web plates, multi-web plates having high fractureresistance under stress due to hailstones is achieved. Accordingly,typical stress resistance of the multi-web plates in a hail shootingtest using polyamide balls of at least 2 J, preferably at least 5 J, isdesired and achieved. Furthermore, EP-A 0 733 754 additionally equipsthe multi-web plates with functional layers. These functional layersinclude scratch-resistance, anti-reflective, water-spreading orIR-reflective coatings on the outside or the inside of the multi-webplates.

JP-OS 08-53555 describes IR-reflective sheets of acrylic plasticcontaining an impact resistant modifier. The sheets are based oncross-linked emulsion polymers containing butyl acrylate andIR-reflective pigments in amounts ranging from 0.5 to 30 wt. %. Thethickness of the sheets with co-extruded layers or for solid sheets mayrange 10 μm to 5 mm. Working the pigments into an acrylic plasticmodified to be impact-resistant takes is achieved by utilizing twosteps. First, the pigment is mixed with the granulate in the dry state.Then, the mixture is extruded to form a granulate.

JP-OS 08-52335 describes IR-reflective sheets or containingpolycarbonate, and having a thickness of at least 0.5 mm. The sheets arealso contain a co-extruded layer of an acrylic plastic modified to beimpact-resistant. Further, the sheets contain IR-reflective pigments inamounts ranging from 0.5 to 20 wt. %. The co-extruded layers havethicknesses ranging from 20 to 300 μm. Working the pigments into theacrylic plastic modified to be impact-resistant is achieved by utilizingtwo steps. First, the pigment is mixed with the granulate while dry in atumbler mixer. Then the mixture is extruded to form a granulate.

Multi-web plates with a high resistance to weathering and a very goodresistance to hail impact are described in EP-A 0 733 754. For anadditional IR-reflective finish on the multi-web plates, EP-A 0 733 754recommends the application of a functional IR-reflective layer asdescribed in EP-A 0 548 822. However, it has been shown that theadditional pigment layer which imparts excellent IR-reflection and isco-extruded, is not as hail-resistant as a plate without the additionalpigment layer. The IR-reflective layer, which can contain 25 wt. %IR-reflective pigment, is more brittle under stress due to hail comparedto that of the underlying impact-resistant polymethyl methacrylate. Thiscan result in the formation of tiny cracks in the IR-reflective layer inthe presence of hail. These cracks are barely visible at first, but canpropagate as the plate is subjected to the effects of weather.Therefore, the IR-reflective layer can start to flake off after sometime.

DE 25 44 245 describes the possibility of working the IR-reflectivepigments into molding masses. Here, the pigments align themselvesparallel to a surface during the course of processing. However, it hasbeen shown that it is not possible to achieve an effect that correspondsto EP-A 0 548 822. The alignment of the particles in a plastic elementmade of an extruded molding mass that contains uniformly distributedIR-reflective pigment is not as good as for a co-extruded or lacqueredseparate layer. Also, the relatively high tendency of these particles tofracture appears to be another problem. The lower rate ofsurface-parallel alignment, combined with a comparatively highproportion of breakage, generally leads to unsatisfactory results.

This is particularly true for plastic elements with a comparativelycomplex geometry deviating from a simple plate shape. During theproduction of such plastic elements, different melt flow directions andshear forces occur during extrusion which force the pigment particlesinto different alignments. Accordingly they are exposed to greateroverall mechanical stress. These shapes include hollow elements such asdouble-web plates and, in particular, complicated hollow elements suchas multi-web plates, latticework plates, etc.

JP-OS 08-53555 and JP-OS 08-52335 describe the extrusion andco-extrusion of acrylic plastic modified to be impact-resistant andcontaining IR-reflective pigments. Since the two components are mixedunder dry conditions, a high proportion of the pigment breaks. Since thepigment fragments reduce transmission and reflect IR waves poorly or notat all, the efficiency of the IR-reflection cannot be optimized withrespect to the amount of pigment used

SUMMARY OF THE INVENTION

One object of the present invention is a process for the manufacture ofa plastic element.

Another object of the present invention is a process for the manufactureof a plastic elements having resistance to hail.

Another object of the invention is a process for the manufacture of aplastic element having degree of light transmission for daylight, T anda low total energy passing through the plastic element.

Another object of the invention is a process for the manufacture of aplastic element comprising 0.01 to 2 wt.-% of IR-reflective particlesmade of a lamellar-shaped carrier pigments coated with a metal oxide.

Another object of the invention is a process for the manufacture of aplastic element comprising 5 to 40 wt. % of the IR-reflective particlesand a low-viscosity thermoplastic plastic.

Another object of the invention is a process for the manufacture of aplastic element comprising 5 to 40 wt. % of the IR-reflective particles,a low-viscosity thermoplastic, and a white pigment.

Another object of the invention is a process for the manufacture of aplastic element having a multi-web plate.

Another object of the invention is a process for the manufacture of aplastic element comprising a co-extruded flange of a multi-web plate.

Another object of the invention is a process for the manufacturing aroof or facade comprising a plastic element comprising 5 to 40 wt. % ofthe IR-reflective particles and a low-viscosity thermoplastic plastic.

Another object of the invention is a roof or facade comprising a plasticelement comprising 5 to 40 wt. % of the IR-reflective particles and alow-viscosity thermoplastic plastic.

The objects of the present invention, and others, may be accomplishedwith a process for the manufacture of a plastic element comprising

processing a plastic mixture by means of extrusion or co-extrusion

wherein

producing a pre-mixture of from 5 to 40 wt. % of the IR-reflectiveparticles with a low-viscosity thermoplastic plastic wherein theIR-reflective particles are mixed with the melt of the low-viscositythermoplastic plastic at a temperature of at least 280° C. in apressure-free, non-shearing zone of a twin-screw extruder;

extruding said pre-mixture;

converting said pre-mixture to granulate form;

subsequently mixing in an extruder the granulate directly or as a meltwith a granulate or a melt of a polymethyl methacrylate modified to beimpact-resistant to form a plastic mixture wherein said polymethylmethacrylate comprises a polymer matrix and an agent to modify impactresistance;

extruding or co-extruding the resultant plastic mixture with a melt of athermoplastic plastic into an extrudate having a desired shape; and

cooling said extrudate having a desired shape.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

As discussed above, a need exists for a process of manufacturingIR-reflective plastic elements with a high resistance to weathering. Inparticular, a process of manufacturing IR-reflective plastic elementsthat are hail-resistant is required.

The present invention fulfills this need by providing a process for themanufacturing of a translucent, IR-reflective plastic element. Thiselement comprises an impact-resistant thermoplastic plastic. Thethermoplastic plastic comprises from 0.01 to 2 wt. % of IR-reflectiveparticles. The IR-reflective particles are made of a lamellar-shapedcarrier pigment coated with a metal oxide.

The processing comprises production of the plastic mixture by extrusionor co-extrusion. First, a pre-mixture containing from 5 to 40 wt. % ofthe IR-reflective particles with a low-viscosity thermoplastic plasticis produced. The pre-mixture is generated by mixing the IR-reflectiveparticles with the melt of the low-viscosity thermoplastic plastic at atemperature of at least 280° C. in a pressure-free, non-shearing zone ofa twin-screw extruder. This mixture is then extruded and converted togranulate form. The resultant granulate is mixed in an extruder directlyor as a melt with a granulate or a melt of a polymethyl methacrylatemodified to be impact-resistant. The granulate or a melt of polymethylmethacrylate contains a polymer matrix and an agent to modify impactresistance. The resultant plastic mixture is then extruded orco-extruded with another melt of a thermoplastic plastic. The describedextrusion or co-extrusion can be modified to produce an extrudate havinga desired shape. The desired plastic element is obtained from theextrudate after cooling.

The above-mentioned pigment in the granulate form does not break easilyif the IR-reflective particles are mixed with the melt of thelow-viscosity thermoplastic plastic at a temperature of at least 280°C., in a pressure-free, non-shearing zone of a twin-screw extruder. Theplastic elements manufactured according to the above process have aresistance to hail that is elevated compared to plastic elementscontaining only impact-resistant polymethyl methacrylate and lacking theIR-reflective pigment. Further, the plastic elements manufacturedaccording to the above process may contain a reduced amount ofimpact-resistance modifier contained in the molding mass. Since theagent to modify impact resistance is always more costly to produce thanthe polymethyl methacrylate matrix, the process according to the presentinvention results in cost savings.

As compared to the known multi-web plates of polymethyl methacrylatecontaining a coextruded IR-reflective finish, the process according tothe present invention manufactures plastic elements with improved hailresistance, thereby improving long-term resistance to weather and/orhail. Further, the present invention does not require co-extrusionlayers with a high proportion of pigment. Therefore, the production ofplastic elements with a risk of increased brittleness under the effectof hail and crack formation resulting therefrom is avoided by thepresent invention.

The present invention also provides a process for the manufacturing of atranslucent, IR-reflective plastic element. The plastic elementaccording to the present invention comprises entirely animpact-resistant thermoplastic plastic. The impact-resistantthermoplastic plastic contains from 0.01 to 2 wt. %, preferably 0.1 to1.5, especially preferably 0.5 to 1.3 wt. %, of IR-reflective particles.The ranges for the quantities of IR-reflective particles include allspecific values and subranges therebetween, such as 0.02, 0.05, 0.1,0.2, 0.4, 0.8, 1.0, 1.1, 1.2, 1.4, and 1.8 wt. %. The particles are madeof a lamellar-shaped carrier pigment coated with a metal oxide.

The process according to the present invention takes place by means ofextrusion of molding masses. First, a premixture comprising alow-viscosity thermoplastic plastic and from 5 to 40 wt. % of theIR-reflective particles is produced. The ranges for the quantities ofIR-reflective particles include all specific values and subrangestherebetween, such as 10, 15, 20, 25, 30, and 35 wt. %. TheIR-reflective particles are mixed with the melt of the low viscositythermoplastic plastic at a temperature of at least 280° C., preferably290° C. to 320° C. The ranges for the quantities of the temperatureinclude all specific values and subranges therebetween, such as 295,300, 305, 310, and 315° C.

The IR-reflective particles and low viscosity thermoplastic plastic maybe mixed in a pressure-free, non-shearing zone of a twin-screw extruder.Preferably, the twin-screw extruder has screws that rotate in oppositedirections. Accordingly, the mixture of IR-reflective and low viscositythermoplastic plastic is extruded and converted to granulate form.Subsequently, the granulate is mixed directly or as a melt in anextruder with a granulate of a polymethyl methacrylate modified to beimpact-resistant. The granulate of a polymethyl methacrylate modified tobe impact-resistant contains a polymer matrix and an agent to modifyimpact resistance. The plastic mixture is extruded or co-extrudedtogether with another melt of a thermoplastic plastic, in a desiredshape. The desired plastic element is obtained from the resultingextrudate after cooling.

In the inventive process, it is preferred to mix the granulate of thepre-mixture with the granulate of the one polymethyl methacrylatemodified to be impact-resistant, and jointly melt this dry mixture whenit is placed in the extruder because it is particularly gentle for theIR-reflective pigments obtained. The granulate of the pre-mixture canalso be added to the melt of the polymethyl methacrylate modified to beimpact-resistant. However, it is difficult to achieve a uniformdistribution in the mass without breaking a high proportion of thepigments. It is also possible, but less preferred, to melt thegranulates separately, e.g. in a main extruder and a secondary extruder,and subsequently combine the melt flows in one extruder, e.g. the mainextruder. It appears to be less gentle for the pigments if thepre-mixture is melted in its concentrated form and used in this forminitially.

The proportion of breaking within the IR-reflective pigment can bereduced if a granulate is produced from the pre-mixture. Here, thegranulate may be obtained by breaking off the extrudate at atemperature, i.e. surface temperature of at least 50, preferably at 60to 90° C. The ranges for the quantities of the temperature include allspecific values and subranges therebetween, such as 65, 70, 75, 80, and85° C. The granulate still possesses a certain softness in thistemperature range, thereby keeping the breaking within the IR-reflectivelow during the step of breaking-off the granulate from the extrudatedescribed above.

Low-viscosity thermoplastic plastics to be used according to the presentinvention may be those having a melt viscosity in the range of 100 to3500, preferably 200 to 1000 Pas measured according to the processdescribed in DIN 54 811, i.e. Process B 220° C./5 MPa (die L/D=4:1). Theranges for the quantities of the melt viscosity include all specificvalues and subranges therebetween, such as 200, 500, 750, 1000, 1500,2000, and 3000 Pas.

The melt viscosity at the processing temperature is preferably 20 to80%, more preferably 40 to 60%, lower in comparison with the meltviscosity of the polymethyl methacrylate matrix that is present in theimpact-resistant polymethyl methacrylate. The ranges for the quantitiesof the melt viscosity at the processing temperature include all specificvalues and subranges therebetween, such as 25, 30, 35, 40, 45, 50, 55,60, 65, 70, and 75% lower in comparison with the melt viscosity of thepolymethyl methacrylate matrix that is present in the impact-resistantpolymethyl methacrylate.

Polymethyl methacrylate is preferably a low-viscosity thermoplasticplastic. The melt viscosity can be 200 to 300 Pas. Suitable melt indicesas determined according to ISO 1133 (230° C./3.8 kg) can lie in therange of 6 and 40, preferably 10 to 30 g/10 min. The ranges forquantities of the melt indices include all specific values and subrangestherebetween, such as 10, 15, 20, 25, 30, and 35 g/10 min. Theweight-average molecular weight, Mw, may lie in the range of 5×10⁴ to1.5×10⁵. The ranges for the quantities of the weight-average molecularweight include all specific values and subranges therebetween, such as6×10⁴, 7×10⁴, 8×10⁴, 9×10⁴, 1.0×10⁵, 1.1×10⁵, 1.2×10⁵, 1.3×10⁵ and1.4×10⁵. The polymethyl methacrylate according to the present inventioncontains from 80 to 96, preferably 84 to 96 wt. % methyl methacrylateunits. The ranges for the quantities of the methyl methacrylate includeall specific values and subranges therebetween, such as 81, 82, 83, 84,85, 86, 87, 88, 89, 90, 91, 92, 93, 94, and 95 wt. %. Further, thepolymethyl methacrylate according to the present invention contains from8 to 20, preferably 4 to 16 wt. % of softer monomers. The ranges for thequantities of the softer monomers include all specific values andsubranges therebetween, such as 9, 10, 11, 12, 13, 14, 15, 16, 17, 18,and 19 wt. %. Examples of softer monomers include but are not limited tohydroxyethyl methacrylate, ethyl acrylate, butyl acrylate, or preferablymethyl acrylate.

The desired flow behavior of the thermoplastic plastic can also beachieved by mixing plastics of high viscosity with plastics with a verylow viscosity, or so-called flow improving agents.

In the present invention, a relatively small amount of the pre-mixturecontaining the lamellar-shaped carrier pigment may be added to thepolymethyl methacrylate modified to be impact-resistant. Therefore,low-viscosity thermoplastic plastics can be used for the pre-mixture, aswell as polymethyl methacrylate, as long as the properties of thepolymethyl methacrylate modified to be impact-resistant are notcompromised or insignificantly impaired. An example of a low-viscositythermoplastic plastic is, but not limited to, polyethylene.

IR-reflective pigments to be used according to the present invention maybe, but not limited to, IR-reflective particles of carrier pigmentscoated with a metal oxide. Examples of such IR-reflective particles ofcarrier pigments coated with a metal oxide are those described in any ofDE 25 44 245 B2, EP-A 548 822, DE 196 18 569 A1. Further IR-reflectivepigments to be used according to the present invention may be, but notlimited to, so-called pearl-luster pigments. Pearl-luster pigments havea layer-shaped or lamellar-shaped structure. As a rule, they have adiameter of 20 to 100 μm. The ranges for the quantities of the diameterinclude all specific values and subranges therebetween, such as 25, 30,35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, and 95 μm.

Infrared reflection of IR-reflective pigments is based on a dualreflection of light at the top and bottom of the particles, which may bealigned parallel to a surface. Depending on the thickness of theparticles and the wavelength of the incident light, rays of lightreflected at the top and the bottom of the particle can either amplifyor cancel each other by interference. A amplification of the reflectedradiation occurs when the incident beams hit the surface at aperpendicular angle and ifd=(2x−1)L _(r)/4nwhere d is the thickness of the particle, X=1, L_(r) is the wavelengthof the reflected radiation, and n is the index of refraction of theparticle at this wavelength. In contrast, cancellation or weakening ofthe reflected light occurs ifd=(x−1)L _(t)/2nwhere here x=2 and L_(t) is the wavelength of the light that in thiscase is not reflected but rather passes through the pigment. Combiningthe two equations produces the following equation:L_(r)=2 L_(t).This means that at a certain layer thickness d, light with thewavelength L_(r) is reflected most strongly, and light with half thatwavelength L_(t) is mostly allowed to pass through the IR-reflectivepigment. In the present invention, a thickness of the particle can beselected in a manner that allows visible light to pass through theparticle, while infrared light is most strongly reflected by theparticle.

Various IR-reflective pigments are known that fulfill the ratio ofthickness and index of refraction desired by the present invention. Suchpigments include, but is not limited to, titanium dioxide. In particularanatase type titanium dioxide is preferred. The IR-reflective pigmentsaccording to the present invention include basic lead carbonate orbismuth oxychloride. Rutile type titanium dioxide, which may beprecipitated on mica particles or similar mineral substances with alamella shape, is particularly advantageous as an IR-reflective pigmentaccording to present invention. Rutile type titanium dioxide may be usedin light-scattering coatings that are particularly well suited for alltypes of roof glazing and skylights. In contrast to anatase typetitanium dioxide, rutile type titanium dioxide does not catalyticallyattack the plastic matrix of the present invention, thereby resulting ina weather-resistant, long-life product. Products fractionated in sizecontaining pigment particles of an average diameter or grain size offrom 5 to 25 μm, are particularly suitable, since they tend to breakless during processing. The ranges for the quantities of the averagediameter or grain size include all specific values and subrangestherebetween, such as 7, 9, 11, 13, 15, 17, 19, 21, and 23 μm. Laserlight diffraction may be used to measure the average diameter or grainsize of the pigment particles. Preferably at least 95%, preferably 98%,of the particles may have a size less than 25 μm.

IR-reflective particles may be used where a carrier pigment is coatedwith a layer of TiO₂ with a thickness of 90 to 150 nm, preferably 100 to140 nm (only the TiO₂ layer is then considered to be the layer thicknessd, not the substratum of mica). The ranges for the quantities of thelayer thickness include all specific values and subranges therebetween,such as 95, 100, 105, 110, 115, 120, 125, 130, and 135 nm. An example ofa carrier pigment is mica.

IR-reflective particles according to the present invention may contain acarrier pigment coated with alternating layers of metal oxide. Examplesof IR-reflective particles containing a carrier pigment coated withalternating layers of metal oxide are described in DE 196 18 569 A1. DE196 18 569 A1 describes multi-layer interference pigments containingtransparent carrier materials coated with alternating layers of metaloxides with a low and a high index of refraction, where the differencein the index of refraction is at least 0.1. Accordingly, carrier pigmentcan be provided with an alternating layer of TiO₂/SiO₂/TiO₂, where thetotal of the layer thicknesses can lie in the range of 150 to 300 nm(the commercially available pearl-luster pigment AC 870, manufactured byMerck KGaA, Darmstadt, Germany, is suitable, for example). The rangesfor the quantities of the total of the layer thicknesses include allspecific values and subranges therebetween, such as 160, 180, 200, 220,240, 260, and 280 nm.

Examples of polymethyl methacrylate modified to be impact-resistantaccording to the present invention and their production are described inEP-A 0 733 754.

The polymethyl methacrylate modified to be impact-resistant may be builtup. An example of building up a polymethyl methacrylate modified to beimpact-resistant is producing a polymethyl methacrylate comprising:

p1) 4 to 30 wt.-% of an elastomer, or E, phase; and

p2) 70 to 96 wt.-% of a thermoplastic matrix, or M, phase of polymethylmethacrylate, where the sum of p1)+p2) comes to 100 wt. %. Further, thepolymethyl methacrylate modified to be impact-resistant may contain upto 20 parts by weight of suitable comonomer particles with reference to100 parts by weight of the total polymer, P. The polymethyl methacrylatemodified to be impact-resistant may contain indices of refraction of theelastomer phase E and the matrix phase M that differ from one another bya maximum of n≦0.02.

The elastomer phase of a cross-linked polymer phase may contain 60 to99.9 parts by weight alkyl acrylate and/or aryl acrylate, 0.1 to 10parts by weight of suitable crosslinking agents and, if necessary, 0 to30 parts by weight of suitable monofunctional ethylene-unsaturatedmonomers.

Preferably, C₂–C₁₀ alkyl acrylates are used as the alkyl acrylates.Examples of such C₂–C₁₀ alkyl acrylates include but are not limited toethyl acrylate, propyl acrylate, iso-propyl acrylate, amyl acrylate,hexyl acrylate, octyl acrylate, and decyl acrylate. C₂–C₁₀ alkylacrylates especially preferred by the present invention are butylacrylate and 2-ethylhexyl acrylate. Other preferred acrylates are phenylacrylate, 2-phenylethyl acrylate, 3-phenyl-1-propyl acrylate,2-phenoxyethyl acrylate, 2-phenoxyethoxyethyl acrylate, and especiallybenzyl acrylate.

The cross-linking agents are generally compounds with at least twoethylene-unsaturated, radically polymerizable radicals. Examples ofcompounds with two ethylene-unsaturated, radically polymerizableradicals include but are not limited to (meth)acrylic esters of diols,such as ethylene glycol di(meth)acrylate or 1,4-butane dioldi(meth)acrylate, aromatic compounds such as divinyl benzene. Further,compounds with at least one allyl group are preferable as cross-linkingagents. An example includes, but is not limited to allyl (meth)acrylate.The cross-linking agents may include those compounds having three ormore ethylene-unsaturated, radically polymerizable radicals. Examplesinclude, but are not limited to, triallyl cyanurate, trimethylol propanetri(meth)acrylate, and pentaerythritetra (meth)acrylate. Other examplesof the cross-linking agents to be used according to the presentinvention are those described in U.S. Pat. No. 4,513,118.

The index of refraction of the elastomer phase is generally lower thanthat of the matrix phase M. Therefore, the comonomers that may becontained in 0 to 30 parts by weight in the elastomer phase primarilyserve to make the index of refraction of the elastomer phase moresimilar to that of the matrix phase, M. Therefore, the present inventionprefers comonomers with comparatively high indices of refraction.Examples of such comonomers are radically polymerizable aromaticcompounds such as vinyl toluene, styrene, and α-methyl styrene. Thesecomonomers are to be used in amounts that ensure they do not impair theweather resistance of the impact-resistant polymethyl methacrylate.

The matrix phase, M, of may be covalently bonded to the elastomer phase,and contain at least 5 wt. % of a polymethyl methacrylate, P. Thepolymethyl methacrylate may contain from 80 to 100 parts by weight ofmethyl methacrylate units, and may have a glass transition temperatureof at least 70° C. Furthermore, the polymethyl methacrylate may containfrom less than or equal to 20 parts by weight of additionalethylene-unsaturated, radically polymerizable comonomer unit. An exampleof a preferable ethylene-unsaturated, radically polymerizable comonomerunit is alkyl (meth)acrylates with 1 to 4 carbon atoms in the alkylradical. The average molecular weight, MW, of the polymethylmethacrylate may be between 10⁴ and 10⁶, preferably between 3×10⁴ and5×10⁵ Dalton. The ranges for the quantities of the average molecularweight of the polymethyl methacrylate include all specific values andsubranges therebetween, such as 4×10⁴, 6×10⁴, 8×10⁴, 1.0×10⁵, 1.5×10⁵,2.0×10⁵, 2.5×10⁵, 3.0×10⁵, 3.5×10⁵, 4.0×10⁵, and 4.5×10⁵ Dalton. Themolecular weight of the polymethyl methacrylate may be determined fromtechniques described by H. F. Mark et al. in Encyclopedia of PolymerScience and Engineering, 2nd edition, Vol. 10, pages 1 ff., J. Wiley,New York, (1989).

The elastomer phase may be a component of a two-stage or multi-stageemulsion polymerizate containing the polymethyl methacrylate that formsthe matrix phase in an outer sheath. Preferred emulsion polymerizatesare those having at least a three-stage structure. Such emulsionpolymerizates contain a core of polymethyl methacrylate, a first shell,S1, of the elastomer phase, and a second shell, S2, of the polymethylmethacrylate, and may contain additional shells corresponding to shellsS1 and S2. The impact-resistant polymethyl methacrylate may contain from5 and 70 wt. %, preferably from 10 and 50 wt. % of an emulsionpolymerizate. The ranges for the quantities of the emulsion polymerizatecontained by the impact-resistant polymethyl methacrylate include allspecific values and subranges therebetween, such as 10, 15, 20, 25, 30,35, 40, 45, 50, 55, 60, and 65 wt. %. Polymethyl methacrylate plasticnot contained in the latex particle may constitute the remaining weightproportions of the impact-resistant polymethyl methacrylate.

The impact-resistant polymethyl methacrylate may be produced by mixingthe emulsion polymerizate with the polymethyl methacrylate. The emulsionpolymerizate may be mixed with the polymethyl methacrylate by means ofconstant substance polymerization, in the melt. Subsequently, theaqueous phase and the emulsifier are removed. Before mixing the emulsionpolymerizate with the polymethyl methacrylate, the emulsion polymerizatemay be isolated from the aqueous phase. The emulsion polymerizatecontain latex particles that may have a diameter of from 0.1 and 3 μm,preferably between 0.15 and 1 μm. The ranges for the diameter of thelatex particles include all specific values and subranges therebetween,such as 0.15, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2,2.4, 2.6, and 2.8 μm. An example of the structure of such latexparticles and the isolation of the emulsion polymerizate for two-stageemulsion polymerizates is described in EP patent 0 033 999 (U.S. Pat.No. 4,543,383). An example of the structure of such latex particles andthe isolation of the emulsion polymerizate for three-stage emulsionpolymerizates is described in EP patent 0 113 925 (U.S. Pat. No.4,513,118).

It is practical to work in the neutral or slightly acidic pH rangeduring aqueous emulsion polymerization. The use of long-chain alkylsulfates or alkyl sulfonates as emulsifiers is advantageous in suchprocesses. Azo compounds, i.e. organic or inorganic peroxides may beused as polymerization initiators in such processes. Examples of suchazo compounds are persulfates. The polymerization initiator may be usedin the process at amounts ranging from 10⁻³ to 1 wt. %, with referenceto the monomers. The ranges for the amount of polymerization initiatorinclude all specific values and subranges therebetween, such as 2×10⁻³,4×10⁻³, 6×10⁻³, 8×10⁻³, 2.5×10⁻², 5.0×10⁻², 7.5×10⁻², 0.1, 0.25, 0.5,and 0.75 wt. %.

Molecular weight adjusters may be used to adjust the aforementionedmolecular weight Mw of the polymethyl methacrylate present in theemulsion polymerizate. Examples of such molecular weight adjustersinclude but are not limited to mercapto compounds, such as 2-ethylhexylglycolate or tert-dodecyl mercaptan.

Emulsion polymerizates that are coagulated and freed of water in anextruder are especially preferred by the present invention. The melt maybe divided into several segments in the water-removal zone of theextruder, each of which is conveyed into a separate screw channel. Themelt phase may be compressed into a cohesive melt cake in at least oneof the intake slot of the twin screw within these screw channels,forming a pressure gradient at a closely limited location. The water isallowed to flow off ahead of the border of the melt cake by means ofshear force towards the bottom through at least one take-off opening.During this time, the melt cake is not in contact with a cohesiveaqueous phase, thereby removing the additives and contaminants containedin the water. Consequently the resultant weather-resistant material doesnot tend to yellow as a result of the presence of such additives andcontaminants. A description of such weather-resistant material can befound see in EPA 0 683 028, as well as that resulting from a two-stageprocess in DE 197 18 597 C1.

The plastic elements produced according to the invention contain theplastic mixture obtained according to the process, and have resistanceto damage as a result of hail. The degree resistance to damage as aresult of hail may be measured by the hail impact test described in SIAV280.. The hail impact test described in SIA V280 implements at least 4J of energy, preferably at least 4.5 J, especially preferably at least 5J. Swiss standard SN Construction 564 280, 1996 edition, Test 9,modified the hail impact test using polyamide balls with a diameter ofapproximately 20 mm. Further, Swiss standard SN Construction 564 280,1996 edition, Test 9 is implemented without ice scales. The hailresistance, or H₂₀, is the lowest energy, measured in Joules, possessedby polyamide balls having a diameter of 20 mm which induces fracturingof the sample.

The above described selectivity characteristic number, or SKZ, measuredin T/g as determined in DIN 67 507 may be more than 1.15, preferably atleast 1.2, more preferably at least 1.3, and most preferably at least1.4 T/g. As stated above, T is the degree of light transmission fordaylight, i.e. standard light type light of D65 or T_(D65), of theplastic element. Further, g is the total degree of energy passingthrough the plastic element. Therefore, the SKZ of a plastic element isthe ratio of T/g, i.e. T_(D65)/g.

The plastic element may contain a plastic mixture only or in part. Theplastic element may have a flat sheet or a hollow element structuralgeometry. An example of such a structural geometry is a multi-web plate,preferably a three-web or four-web plate, and most preferably adouble-web plate. Other geometries are preferred by the presentinvention as well, such as web plates with slanted webs. These platesmay be referred to as lattice-work plates.

One example of a plastic element according to the present invention is aplastic element that may contain only the plastic mixture and have theform of a double-web plate. Such plastic elements possess relativelygood SKZ values. In contrast, three-web or four-web plates that consistentirely of a plastic mixture possess a poorer SKZ value in general thanthat of double-web plates. This phenomenon is believed to be due to thedegree of light transmission for daylight (T, i.e. T_(D65)) droppingmore sharply for three-web or four-web plates than the degree of totalenergy pass-through for radiation energy (g). Therefore, the SKZ valuein T/g decreases for three-web or four-web plates.

The plastic element may contain the plastic mixture in part. Such aplastic element contains a partial proportion of the plastic mixturethat can be a co-extruded flange of a multi-web plate. In this example,the co-extruded flange may have a thickness ranging from 1 to 6,preferably 2 to 4 mm. The ranges for the thickness of the co-extrudedflange include all specific values and subranges therebetween, such as1.5, 2.0, 2.5, 3.0, 3.5, 4.0, and 4.5 mm. Co-extruded flanges of suchthickness can be used to produce any multi-web plates, three-web andfour-web plates because the maintain good SKZ value and resistance tohail impact resistance. The co-extruded flange of such plates is thickenough to retain the desired SKZ values even in combination with lowconcentrations of IR-reflective particles.

It is practical if the plastic element has a degree of lighttransmission for daylight (T, i.e. T_(D65)) in the range of 10 to 70,preferably 15 to 55, most preferably 20 to 40%, depending on theirpurpose of use. The ranges for the degree of light transmission fordaylight of the plastic element includes all specific values andsubranges therebetween, such as 15, 20, 25, 30, 35, 40, 45, 50, 55, 60,and 65%.

A preferred use of the plastic element is for the production of aroofing or facade element and light strips in stairwells, etc. Examplesof roofing or facades include, but is not limited to, greenhouse orwinter garden roofs .

The plastic elements according to the present invention have a pinkcolor appearance with a gleam similar to mother-of-pearl on the sidefacing the light. This pink color appearance occurs in commerciallyavailable plastic elements with an IR-reflective finish. Looking throughthe plastic elements against the light, the color impression isgreenish. In many cases, the greenish color impression is reduced byadding a light-scattering pigment. An example of a light-scatteringpigment is a white pigment, e.g. barium sulfate. Such light-scatteringpigments may be added in amounts of 0.5 to 5 wt. %. The ranges for theamounts of light-scattering pigments includes all specific values andsubranges therebetween, such as 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, and4.5 wt. %. Adding these light-scattering pigments to the element reducesthe glare effect when the sun is shining through the element by causingthe light to be scattered.

Surprisingly, it is also found that the resistance to hail impact of aplastic element does not decrease if a white pigment, e.g. bariumsulfate (BaSO4) is present, in combination with an agent to modifyimpact resistance and IR-reflective pigment. In fact the resistance tohail impact of a plastic element can actually increase by adding thewhite pigment and agent. The white pigment, as well as the IR-reflectivepigment, may be made added during the extrusion process for productionof the plastic element according to the invention as a concentratedpre-mixture in granulate form. The granulate may contain from 10 to 30wt. % white pigment. The ranges for the amounts of white pigment in thegranulate includes all specific values and subranges therebetween, suchas 12, 14, 16, 18, 20, 22, 24, 26, and 28 wt. %. Further, the whitepigment may also be added in powder form during the extrusion process.

The process according to the invention is explained in more detail inTables 1 and 2 and in the following examples.

EXAMPLES

The present invention is explained in more detail with the aid of thefollowing embodiment examples. As can be seen from the followingexamples, the process according to the present invention produced aplastic element having a high degree of resistance and a highselectivity characteristic number, SKz.

Example 1

Production of a pre-mixture, in granulate form, of a low-viscositypolymethyl metbacrylate melt and IR-reflective pigment.

The pre-mixture is produced by working 25 wt.-% of the pigment Iriodin®9223, Rutil Perllila (manufactured by Merck KGaA, Darmstadt, Germany)into the melt of a polymerizate containing 91 wt. % methyl methacrylateand 9 wt.-% methyl acrylate, at 300° C. The polymerizate is melted andtransported in a twin-screw extruder with screws running in the samedirection (D=34, model by Leistritz). The pigment is added via a sidefeed, without pressure, in a pressure-free, non-shearing extruder zone,via a screw metering system that works volumetrically. Production of agranulate with a length of 2.5 to 3.5 mm and a diameter of 2 to 3 mmoccurs at 80° C. (surface temperature) by granulation.

Example 2

Production of 16 mm double-web plates from the pre-mixture from Example1 and polymethyl methacrylate modified to be impact-resistant.

a) Polymethyl methacrylate modified to be impact-resistant.

Polymethyl methacrylate modified to be impact-resistant containing apolymer matrix of a polymerizate having 97 wt. % methyl methacrylate and3 wt. % methyl acrylate and a proportion of 15 wt.-% polybutyl acrylateis obtained by mixing 64 wt. % polymethyl methacrylate with 36 wt. % ofa core-shell emulsion polymerizate with a the first shell containingcomposition containing 20 parts by weight cross-linked polymethylmethacrylate core and 44 parts by weight cross-linked polybutyl acrylateco-styrene with the same index of refraction as the polymer matrix, anda second shell containing 36 parts by weight polymethyl methacrylate. Acorresponding emulsion polymerizate may be obtained by a processdescribed in EP-A 113 924.

Subsequently, double-web plates with a thickness of 16 mm are producedby means of extrusion. The granulate of the polymethyl methacrylatemodified to be impact-resistant and the granulate of the pre-mixturefrom Example 1 are mixed with the IR-reflective pigment in a ratio of133:1, and extruded through an extrusion die for the double-web plate ina twin-screw extruder, at about 240 to 260° C. After exiting from theextrusion die, the extrudate is stabilized in a vacuum calibration stepand cooled.

Example 3

A double-web plate made of impact-resistant polymethyl methacrylate withwhite pigment (BaSO4) and the addition of the IR-reflective pigmenttakes place in the granulate form of the pre-mixture described. Thewhite pigment, BaSO₄, contained at 20 wt. % in a polymerizate of 97 wt.% methyl methacrylate and 3 wt.-% methyl acrylate was added in a finalconcentration of 2 wt. %.

Example 4

A double-web plate made of impact-resistant polymethyl methacrylatewithout white pigment (colorless). The addition of the IR-reflectivepigment takes place in the granulate form of the pre-mixture described.

Comparative Example 5

A double-web plate made of impact-resistant polymethyl methacrylate withwhite pigment and without IR pigment.

The white pigment, BaSO₄, contained at 20 wt. % in a polymerizate of 97wt. % methyl methacrylate and 3 wt. % methyl acrylate, was added in afinal concentration of 2 wt. %.

Comparison Example 6

A double-web plate made of impact-resistant polymethyl methacrylate withwhite pigment. The addition of the IR-reflective pigment takes place byadding the bulk material (in the dry form and without a pre-mixture intothe melt of the polymethyl methacrylate modified to be impact-resistant.

Table 1 summarizes the properties of the double-web plates from Examples3 to 6:

TABLE 1 IR pigment IR pigment addition from addition without WhiteT_(D65) SKZ = Hail H₂₀ Example pre-mixture pre-mixture Pigment [%] g[%]T_(D65)/g [J] 3 + − + 47.3 38.0 1.24 4.4 4 + − − 52.2 39.7 1.31 7.3 5 −− + 76.0 72.0 1.04 2.9 6 − + + 26.7 33.8 0.79 3.9

Example 7

The effect of the melt temperature during the production of apre-mixture, containing IR-reflective pigment.

A pre-mixture is produced analogous to Example 1, except that the melttemperature is only 265° C. when the pigment is worked into the melt.

The granulates from Example 1 and 7 are melted in a thin layer andexamined under a microscope.

In addition, the melt viscosity is determined as described in DIN 54811, Process B 220° C./5 MPa (die L/D=4/1).

The granulates are melted in an extruder and applied, in a co-extrusionprocess (see, for example, EP-B 548 822, particularly Example 4) asco-extrusion layers with a thickness of approximately 30 μm, ontodouble-web plates of polymethyl methacrylate, with a thickness of 16 mm,extruded at the same time. The selectivity characteristic numbers(SKZ=T/g, i.e. T_(D65)/g) of the plates obtained are determined asdescribed in DIN 67 507. Table 2 lists the results.

TABLE 2 Example 1 7 Melt temperature during 300° C. 265° C. productionof the pre-mixture Microscopy Only a small Clearly more pigment amountof breakage than in Example pigment 1, many microparticles, breakagepigment rounded off visible Melt viscosity according to 717 Pas 935 PasDIN 54 811, Process B 220° C./5 MPa, die L/D = 4/1 SKZ = T_(D65)/g  1.36 1.24

The present application claims priority to German Application No. DE 10122 315.3, filed on May 8, 2001, which is hereby incorporated byreference in it entirety.

Numerous modifications and variations on the present invention arepossible in light of the above teachings. It is, therefore, to beunderstood that within the scope of the accompanying claims, theinvention may be practiced otherwise than as specifically describedherein.

Unless specifically defined, all technical and scientific terms usedherein have the same meaning as commonly understood by a skilled artisanin biochemistry, chemistry, and materials science.

All methods and materials similar or equivalent to those describedherein can be used in the practice or testing of the present invention,with suitable methods and materials being described herein. Allpublications, patent applications, patents, standards, and otherreferences mentioned herein are incorporated by reference in theirentirety. In case of conflict, the present specification, includingdefinitions, will control. Further, the materials, methods, and examplesare illustrative only and are not intended to be limiting.

1. A process for the production of a plastic element, wherein saidplastic element comprises an impact-resistant, thermoplastic plastic,and from 0.01 to 2 wt. % of IR-reflective particles comprisinglamellar-shaped carrier pigments coated with a metal oxide, comprising:mixing said IR-reflective particles with a melt of a low-viscositythermoplastic plastic at a temperature of at least 280° C. in apressure-free, non-shearing zone of a twin-screw extruder to form apre-mixture comprising from 5 to 40 wt. % of said IR-reflectiveparticles; extruding said pre-mixture; converting said pre-mixture togranulate form or a melt; mixing said granulate or melt of thepremixture with a granulate or a melt of a polymethyl methacrylatemodified to be impact-resistant to form a plastic mixture wherein saidpolymethyl methacrylate comprises a polymer matrix and an agent tomodify impact resistance; extruding or co-extruding the resultantplastic mixture with a melt of a thermoplastic plastic into an extrudatehaving a desired shape; and cooling said extrudate.
 2. The processaccording to claim 1, wherein the granulate of the pre-mixture isproduced by breaking off said granulate from an extrudate of saidpre-mixture at a temperature of at least 50° C.
 3. The process accordingto claim 1, wherein said IR-reflective particles comprise at least oneearner pigment.
 4. The process according to claim 3, wherein the carrierpigment is coated with a TiO₂ layer.
 5. The process according to claim4, wherein the TiO₂ layer comprises a thickness of from 90 to 150 nm. 6.The process according to claim 3, wherein said carrier pigment is coatedwith at least one alternating layer of metal oxide.
 7. The processaccording to claim 6, wherein said alternating layer comprisesTiO₂/SiO_(b 2)/TiO₂.
 8. The process according to claim 6, wherein saidalternating layer comprises a total layer thicknesses of from 150 to 300nm.
 9. The process according to claim 1, wherein said IR-reflectiveparticle comprises mica laminae.
 10. The process according to claim 9,wherein said mica laminae comprises at least one layer of TiO₂.
 11. Theprocess according to claim 10, wherein said layer of TiO₂ comprises athickness of from 90 to 150.